[tex4ht] problem with mathjax

[Nasser M. Abbasi]

Hello experts;

The following MWE, from old code, does not work when
compiling in mathjax mode

-------------
\documentclass[12pt]{article}
\usepackage{amsmath}
\begin{document}

vector $\mathbf{\tau}$ as
\[
{B\mathbf{\tau}=}\mathbf{b}_{1}{\tau}_{1}\mathbf{+b}_{1}{\tau}_{1}%
\mathbf{+\cdots+b}_{N}\ {\tau}_{N}%
\]
\end{document}
------------------------------

Using make4ht foo.tex "htm,mathjax"

But compiles OK in svg or default png

Using make4ht foo.tex "htm"

I thought it was \mathbf, but when I changed it to

\[
{B\boldsymbol{\tau}=}\boldsymbol{b}_{1}{\tau}_{1}\boldsymbol{+b}_{1}{\tau}_{1}%
\boldsymbol{+\cdots+b}_{N}\ {\tau}_{N}%
\]

it still did not compile right. Strange since both versions compile OK
in latex and other modes.

Here is screen shot

https://www.12000.org/tmp/011819/error.png

Any suggestion what why mathjax does not like the above?

Thanks
--Nasser